A federal appeals court has temporarily blocked Seattle’s first-in-the-nation law allowing drivers of ride-hailing companies such as Uber and Lyft to unionize over pay and working conditions.

A three-judge panel of the 9th U.S. Circuit Court of Appeals said Friday it was blocking the law pending an appeal by the U.S. Chamber of Commerce, which challenged the law on behalf of the companies.

The judges offered no explanation for why they granted the organization’s request to block the law until the case is decided, but the standards for issuing such an order typically include a determination that the appealing party is likely to win the case and that it is likely to suffer “irreparable harm” unless the court steps in.

Brooke Steger, Uber’s general manager for the Pacific Northwest, called it the right decision.

“The Court will now have the time to hear from all parties and carefully consider the unique questions raised by the City’s ordinance,” Steger said in an emailed statement. “There is a tremendous amount at stake in this case, namely the rights and livelihoods of thousands of drivers and the fate of a transportation option that many Seattle residents and visitors have come to rely on. We remain confident the Court will find the City overreached in its effort to protect taxi companies and help the Teamsters.”

The 2015 law requires companies that hire or contract with drivers of taxis, for-hire transportation companies and app-based services to bargain with them if a majority show they want to be represented.

The law has been seen as a test case for the changing 21st-century workforce, with the city arguing that letting drivers bargain over their working conditions will make the industry safer and more reliable and protect workers from unjust terminations. Seattle has been a national leader on workers’ rights, gradually raising its minimum wage to $15 and requiring most employers to provide paid sick leave.

However, critics argued that it flouted federal labor law and would have dire consequences for the popular services in Seattle. Two federal court cases challenged the measure, one by the chamber and one by 11 drivers represented by the National Right to Work Legal Defense Foundation.

U.S. District Judge Robert Lasnik initially placed the law on hold pending those challenges. But last month, he rejected both cases and said he would allow the city to begin implementing the measure.

“The city looks forward to continuing to defend this publicly important law on appeal,” said assistant city attorney Michael Ryan.